The present invention relates to a packaging arrangement for an onboard spacecraft computer to conduct experiments in the hostile environment of outer space. The computer is designed for use in connection with an onboard computer to conduct multidisciplinary research on such programs as the NASA Spacelab. The packaging arrangement utilizes very large scale integration (VLSI) circuits which have direct contact therewith to dissipate heat from the VLSI circuits and other heat producing items through a housing to a cold plate. Also the packaging arrangement eliminates electromagnetic interference and helps dissipiate galactical radiation especially of the x-ray frequency type. The subject invention is lightweight and economical, plus has additional features of (1) ease of access to check out the computer, and (2) reprogrammability of an erasable programmable read only memory (EPROM).